1. Field of the Invention
This invention is directed towards a fixed film, pulsed air process for the treatment of waste water wherein oxygen transferred to the biomass is enhanced by direct contact of the biomass with bubbles entrapped and prolonged within a media bed.
2. Description of the Prior Art
In the treatment and purification of waste waters a number of processes exist which involve the growing of bacteria used to degrade the waste water components either in a suspended culture or on a fixed or movable media. The latter method is commonly known as a fixed film biological process and generally appears to have certain advantages over the commonly used suspended culture or activated sludge processes. One such distinct and well recognized advantage is the ability to develop a greater biomass concentration per unit volume and thereby to decrease the necessary reactor size for such treatment. This has the obvious advantages of reduced land area and capital cost requirements. Another important advantage is directed to the positive control of the biomass inventory which results in a more reliable treatment performance.
Prior to approximately 1970, most fixed film systems consisted of passing waste water over non-submerged rock or plastic media towers followed by a secondary clarification. The utilization of plastic media was looked upon as an improvement over the previously used rock media system since it had an increased surface area per unit volume and a greater void volume to facilitate air flow through the media and improve oxygen transfer to the liquid and therefore to the biomass growth on the media.
A system resulting in similar performance and cost features incorporates the rotation of a biological contactor where the media is attached to a shaft and rotated through waste waters. The waste waters are retained in tanks to insure contact with the biomass on the media. Aeration to the system occurs due to the fact that the rotating media is exposed to atmosphere approximately 60% of the time.
Prior art systems designed to incorporate submerged fixed film application were based on the requirement of using relatively small sized particulate media exhibiting high surface area characteristics in order to increase the fixed film biomass concentration per unit volume and thereby decrease the reactor size. Most of the prior art fixed film designs were upflow systems utilizing a variety of oxygen transfer methods. High rate biological oxygen demand requirement in the reactors of these systems were satisfied by presaturating the feed water with oxygen. Downflow systems are also recognized in the prior art wherein a packed bed fixed film system is utilized and waste water is fed to the top of the bed so that it flows downward through the packed bed media. The intended waste water treatment occurs by solid particle filtration and biological oxidation of soluble organic material by the biomass growing on the media. Specifically, a downflow fixed film biological media reactor has been introduced in France (biological aerated filter) wherein air is introduced into an intermediate location in the filter bed depth and the media depth below the air sparging point is utilized and is necessary for solids filtration.
While submerged fixed film systems are known to have reduced reactor size and capital cost requirement, typical continuous air sparging processes generally result in a greater energy requirement then previously used rock or plastic media towers. Such energy requirements in continuous flow sparged fixed film systems are dependent on the amount of oxygen that could be transferred to the liquid in the reactor from the sparging gas passing upward through the reactor.
The above set forth prior art processes and techniques base their oxygenation design on a fundamental oxygen transfer mechanism known in the prior art as the "two film" theory. Application of this theory, which was established in 1928, generally states that the oxygen is first transfered from a gas bubble into the bulk liquid and the biomass bacterial cells consumes the dissolved oxygen due to diffusion of dissolved oxygen from the liquid to the biofilm rather than from any direct engagement or contact with the gas bubble itself.
Accordingly, there is a recognized need in the prior art for a fixed film waste water treatment system having the advantages of a reduced reactor size and capital cost requirement while at the same time having minimal or at least reduced energy requirements to satisfy the oxygenation needs of the biofilm or system bio-mass.